Engrowe.com has this quick tutorial posted about converting one popular data transfer style (RSS) into another (JSON) using the power of PHP.
Here are a quick set of directions to build your own RSS to JSON proxy using only PHP. You need to download and install two libraries, MagpieRSS for RSS and JSON-PHP for JSON. With these two libraries you can easily create a simple proxy to suit your needs.
The script grabs the contents of the RSS feed and uses the built-in functionality of the MagpieRSS library to re-encode the data into a JSON format. Then, it spits out the result to the browser for consumption yet again...